1. Field of the invention:
The present invention relates to a process for producing a SiC semiconductor device.
2. Description of the prior art:
Semiconductor devices such as diodes, transistors, integrated circuits (IC), large scale integration (LSI) circuits, light emitting diodes, semiconductor lasers, charge coupled devices (CCD), etc., made of semiconductor materials such as silicon (Si), gallium arsenide (GaAs), gallium phosphide (GaP), etc., are in actual use in the fields of electronics.
Silicon carbide (SiC) is a semiconductor material which has a wider forbidden energy gap of 2.2 to 3.3 electronvolts (eV) than the above-mentioned semiconductor materials and is thermally, chemically and mechanically stable and also has a great resistance to radiation damage. Thus, a semiconductor device using SiC is usable under a severe condition (e.g., in high temperature, where great amounts of electrical power are required, and/or in radiation emission environments), where difficulties are encountered with devices made of other semiconductor materials, so that it can be used in an enlarged range of applications for devices requiring a high reliability and high stability.
Despite these many advantages and capabilities, a SiC semiconductor device has not yet been in actual use because the technique still remains to be established for growing high quality SiC crystals having a large surface area with good reproducibility required for the commercial production thereof.
Conventional diodes and transistors have been produced on a laboratory scale using a SiC singlecrystal grown by sublimation (i.e., the Lely method) or the like, and/or a SiC single-crystal film epitaxially grown by chemical vapor deposition, liquid phase epitaxy, etc., on the SiC single-crystal, which are disclosed in R. B. Campbell and H.-C. Chang, "Silicon Carbide Junction Devices", in "Semiconductors and Semimetals", eds. R. K. Willardson and A. C. Beer (Academic Press, New York, 1971) vol. 7, Part B, Chap. 9, P.625-P.683. However, these conventional techniques only provide single-crystals having a small surface area and, moreover, cannot provide single-crystals of a desired size and/or shape. Moreover, with use of these conventional techniques, it is difficult to control the polytype of single-crystals and the concentration of impurities contained in the SiC crystals. Therefore, it is impossible to produce semiconductor devices using SiC single-crystals on a commercial scale.
In recent years, the inventors have completed a process for growing a large-sized single-crystal of silicon carbide of good quality on a single-crystal substrate of silicon by the chemical vapor deposition technique and filed a Japanese Patent Application No. 58-76842 (76842/1983) which corresponds to U.S. patent application Ser. No. 603,454. This process includes growing a thin film of silicon carbide on a silicon substrate by the CVD method at a low temperature and then growing a single-crystal film of silicon carbide on the said thin film by the CVD method at a higher temperature, thereby allowing the production of a large-sized single-crystal substrate of silicon carbide having a high quality on a single-crystal substrate of silicon which is available at a low cost while controlling the polytype, the concentration of impurities, the electric conductivity, the size, the shape or the like of single-crystals. This process is also suitable for the mass-production of such a SiC single-crystal film with high productivity.